A wire bonding capillary is a tube made of ceramics, which is mounted to a tip of a wire-feeding portion of a wire bonding apparatus. In general, each wire bonding capillary has a through bore for feeding a bonding wire, a funnel-shaped bore for guiding the wire to the through bore, and a chamfer formed at an exit of the through bore. Here, the through bore is formed at the smallest diametered portion in each wire passage of a capillary. The chamfer is generally formed to taper having an opening angle of between 45.degree. and 60.degree. ( shown .theta.1, .theta.2 in FIG. 1). Further, the corner between the chamfer and the through bore may be grounded to be round.
An embodiment of Japanese Unexamined Patent Publication No. Shou 59(1984)-191338 discloses the following wire bonding capillary. The capillary, according to the embodiment, has a through bore whose diameter (corresponding to d1 in FIG. 1) is 43 .mu.m and a chamfer whose opening angles( corresponding to .theta.1, .theta.2 in FIG. 1) are 45.degree. and 15.degree..
In Japanese Examined Utility Model Publication No. Hei 1(1989)-42349, the following wire bonding capillary is disclosed as a preferable one; he through bore diameter (corresponding to d1 in FIG. 1) is the wire diameter plus 8-12 .mu.m; each of the opening angles of the chamfers (corresponding to .theta.1, .theta.2 in FIG. 1) is 40-50.degree. and 10-20.degree., respectively; and the chamfer length ( corresponding to h1 in FIG. 1) is the wire diameter.times.0.7-1.5.
However, none of the two prior arts discloses the through bore length and a technology trend for long and low loop wire bonding processes, as described below, and its associated problems.
Recently, in VLSI (Very Large Scale Integration) and the like, miniaturization of chips and multiplication of pins for high integration purposes have been advanced further, so that a need for long and low loop wire bonding processes becomes keen.
When a conventional wire bonding tool is used for carrying out a long and low loop wire bonding process, it is necessary to feed, from the through bore, the wire with a twice length longer than usual. Accordingly, the wire tends to twine and thus to yield a dispersion of the loop height due to sagging and excessive tautening. The sagging of the loop causes the wires to contact each other to lead to a short circuit failure. And also, the excessive tautening of the loop applies excess stress to a neck portion of a bonded ball to lead to a disconnection failure. Both failures are fatal defect on the wire bonding process and have to be completely dismissed.
In view of the above problems, the object of the present invention is to provide a wire bonding capillary, which is suitable for a long and low loop wire bonding process and is able to lower wire slide resistance.